Shell of the pearl layer in the pearl oyster is consisting of minor proteinic organic matrix and crystal of aragonite. This organic matrix had been designated as "Conchiolin" (Fremy, M. E., Recherches chimiques sur les os. Ann. Chem. Phys, 43, 96 (1855)) and have been studied by many persons since then in all its aspects.
See, for example, the publications of:
(1) Cariolou, M. A. & Morse, D. E., "Purification and Characterization of calcium-binding conchiolin shell peptides from the mollusc, Haliotis rufescens, as a function of development", J. Comp. Physiol. B, 157, pp. 717-729 (1988); PA1 (2) Samata, T. & Krampitz G, "Ca-binding polypeptides in oyster shells", Malacologia 22, pp. 225-233 (1981); PA1 (3) Samata, T., "Ca-binding glycoproteins in molluscan shells with different types of ultrastructure", The Veliger 33, pp. 190-201 (1990); PA1 (4) Koji WADA, "Pearl", Association of Jewelogy of Japan (1982); PA1 (5) Weiner, S. & Hood, L., "Soluble protein of the organic matrix of mollusk shells: a potential template for shell formation", Science, 190, pp. 987-989 (1975); PA1 (6) Weiner, S. & Lowenstam, H. A., "Discrete molecular weight components of the organic matrices of mollusc shells", J. exp. mar. Biol. Ecol., 30, pp. 45-51 (1977); PA1 (7) Weiner, S., "Aspartic acid rich proteins: major component of the soluble organic matrix of mollusc shells", Calicif. Tissue Int., 29, pp. 163-167 (1979); and PA1 (8) Weiner, S., "Mollusk shell formation: isolation of two organic matrix proteins associated with calcite deposition in the bivalve, Mytilus calfornianus", Biochemistry, 22, pp. 4139-4145 (1983).
Up to date, although it was reported that one of the main components in the organic matrix of the pearl layer is asparatic acid rich acidic protein in the molecular weight of 50.about.70 kD [See, publications (3) and (7) listed above], its accurate molecular weight and the amino acid sequence thereof have not been reported at all.
Accordingly, as a popular technology for forming pearl wherein a part of shell of Pinctada fucata is coaggulated, cultivation methods depending on environmental (cultural) conditions have been employed over one century or more to cultivate Pinctada fucata for one to two year(s) in a hanging sack in the sea.